Until recently, the only way to evaluate the effectiveness of a support surface was by measuring the tissue interface pressure (TIP). TIP is a vertical force exerted when soft tissue is compressed over the bony prominence that causes capillary closure. This closure can result in ischemia, and subsequent cell death. Pressure, however, is only one part of the pressure-ulcer equation. Another important factor in the development of pressure-ulcers is shear. Shear is a parallel force that occurs when the skin and underlying subcutaneous tissue are pulled taut and over-stretched, causing tissue deformity, obstructing blood flow, and necrosis.
Research has shown that pressure-ulcers are a result of a pressure/shear relationship. (Bennet L. et al. Shear vs. Pressure as Causative Factors in Skin Blood Flow Occlusion. Arch. Phys. Med. Rehab. 1979; 60:309-314) An inverse relationship exits between pressure and shear. The greater the shear, the less pressure required to cause tissue damage. According to the research, the critical ratio is 2:1, which means that it takes twice as much shear force to equal pressure, (1 mmgHg of pressure.apprxeq.2 units of shear. This ratio between vertical pressure and parallel shear force is called, by Gaymar Industries, Inc., the Isolibrium Factor.
A problem with evaluating the Isolibrium Factor was that it was difficult to accurately and effectively measure. The present invention solves this problem.